Bone surface topology mapping and its role in trabecular bone quality assessment using scanning confocal ultrasound

Introduction: Quantitative ultrasound (QUS) has been used to assess non-invasively bone quality, in which ultrasound velocity (UV) is a primary acoustic property. Methods: While UV calculation requires the tissue thickness in the ultrasound path, a bone surface topology mapping (STM) method was developed in this study for enhancing the accuracy of the UV measurement. STM accuracy was verified by both aluminum and a QUS heel phantom, indicating that the STM can determine the phantom thickness within 0.02 mm thickness error and the aluminum calibration step within 0.1 mm thickness error. STM performance was further evaluated using 25 cadaveric human calcanei samples. Results: The UV calculations using STM had a significant better correlation to bone mineral density (BMD) (r=0.75, p<0.05), volume fraction (r=0.72, p<0.05) and modulus (r=0.69, p<0.05) than the UV with fixed thickness. The later correlation coefficients were r=0.64 for BMD, r=0.65 for volume fraction, and r=0.58 for modulus. The nBUA value determined using STM was also highly correlated to BMD (r²=0.74) and modulus (r²=0.62). This was comparable to the correlation result for BUA (BMD: r²=0.76; Modulus: r²=0.64). Conclusion: These results suggested that STM technique in scanning ultrasound is capable of determining calcaneus bone thickness and hence enhancing the accuracy of UV measurement.